A non-contact rotation angle detecting device has been known in the prior art. The non-contact rotation angle detecting device detects a rotation angle of a shaft member in order to detect an operation amount of a brake pedal of a car or the like. The non-contact rotation angle detecting device has, for example, a magnet member that is placed in the shaft member to face a magneto-electric conversion element and is configured to detect the rotation angle of the shaft member in response to a relative rotation of the magnet member with respect to the magneto-electric conversion element. As an example, JP 2007-139458A (Reference 1) described below discloses a “rotation angle detecting device that is provided with a housing which is provided with a magnetic sensor, a pivoting member which is provided with a magnet facing the magnetic sensor and is pivotable with respect to the housing, and the shaft member which is operated to pivot with an operated member, and is configured to be capable of detecting an oscillation angle of the operated member based on a change in an output signal from the magnetic sensor which rotates relative to the magnet” (described in Paragraph [0001] of Reference 1).
JP 2007-93280A (Reference 2) described below discloses a “rotation angle sensor that rotates a radially magnetized disk magnet to sense a horizontal magnetic field which is generated in the disk magnet with X and Y magneto-electric conversion elements placed at right angles to each other and obtains a rotation angle from output values of the X and Y magneto-electric conversion elements” (described in Paragraph [0016] of Reference 2), in which Hall elements are used as the magneto-electric conversion elements (described in Paragraph [0020]).
In Reference 2 described above, the placement of the magneto-electric conversion elements is specified (described in Paragraph [0016]) for the purpose of “providing the rotation angle sensor that achieves cost reduction and structural simplification with the small magneto-electric conversion elements, allows the magneto-electric conversion element to be placed even at a position spaced apart from the center of the disk magnet, and is capable of suppressing an angular error attributable to a relative positional deviation between the magneto-electric conversion element and the disk magnet” (described in Paragraph [0015] of Reference 2). With regard to its specific configuration, the rotation angle sensor is configured, as disclosed in FIG. 1 and described in Paragraphs [0020] and [0021], to be placed to face the X and Y Hall elements which are magneto-electric conversion elements, rotate the radially magnetized disk magnet so as to sense the subsequent horizontal magnetic field with the X and Y Hall elements placed at right angles to each other, and obtain the rotation angle from their output values.
However, in order to suppress the angular error attributable to the relative positional deviation between the magneto-electric conversion element and the disk magnet, not only the placement of the magneto-electric conversion element but also widening a parallel magnetic field provided for the magneto-electric conversion element to the maximum extent possible is effective. In order to reduce manufacturing costs, it is effective to ensure a magnetic flux density required for operating the Hall IC with a magnet that has a small volume. According to the specific configuration of the rotation angle detecting device described in Reference 1 above, a pair of the Hall ICs are stored in a boss portion that is formed to protrude from a housing main body, a pivoting member that is tiltably linked to a shaft member which is pivotally supported by a cover member has a yoke main body and a magnet holder formed of a non-magnetic body material, and a permanent magnet is stored and supported inside the magnet holder as disclosed in FIG. 2 of Reference 1 and described in Paragraphs [0013] to [0016] of Reference 1 while a relationship between the magneto-electric conversion element and the disk magnet according to Reference 2 differs from that according to Reference 1.